Electric circuit breaker with electromagnetic means for opposing contactrepulsion forces



Jan. 30, 1968 P. BARKAN 3,366,900

ELECTRIC CIRCUIT BREAKER WITH ELECTROMAGNETIC MEANS FOR OPPOSING CONTACT-REPULSION FORCES Filed June 16, 1966 .2 Sheets-Sheet 1 PH/L/P BAR/(AN,-

ATTORNEY Jan. 30, 1968 P. BARKAN 3,366,900

ELECTRIC CIRCUIT BREAKER WITH ELECTROMAGNETIC MEANS FOR OPPOSING CONTAC'I-REPULSION FORCES Filed June 16, 1966 2 Sheets-Sheet 2 INVENTOR.

PH/L/P BAR/(AN,

BY fi/wuhwzfmm 1 ATTORNEY United States Patent 3,366,900 ELECTRIC CIRCUIT BREAKER WITH ELECTRG- MAGNETIC MEANS FOR OPPOSING CONTACT- REPULSION FORCES Philip Barkan, Media, Pa., assignor to General Electric Company, a corporation of New York Filed June 16, 1966, Ser. No. 558,008 12 Claims. (Cl. 335-15) This invention relates to an electric circuit breaker and, more particularly, relates to electromagnetic means for opposing the contact-repulsion forces developed when a high current flows through the circuit breaker.

In the usual circuit breaker, the conductive path through the contacts of the circuit breaker is of a generally loop-shaped configuration. Current flowing through this loop-shaped path produces magnetic forces tending to enlarge the loop, and these forces are usually in a direction tending to open the contacts of the breaker. These magnetic opening forces vary in magnitude in accordance with the square of the current flowing through the breaker, and hence during overcurrent and short circuit current conditions, extremely high opening forces can be developed. A more detailed explanation of how these magnetic opening forces are developed is contained in my U.S. Patent 3,225,160, assigned to the assignee of the present invention.

If a circuit breaker is closed when a fault is present on the line, the above-described high magnetic opening forces are abruptly established near the end of a closing stroke. These forces tend to oppose the final portion of the closing stroke, and it is therefore necessary to provide high closing forces in order to overcome this opposing force and complete the closing operation. In conventional circuit breakers, the necessity for providing these high forces for closing against short circuits is a major determinant of the size of the closing mechanism and the mechanism-operator. The higher the closing force required, the larger and more powerful the closing mechanism and operator needed.

An object of my invention is to provide a circuit breaker which can be closed against short circuit currents by a small and relatively weak closing mechanism and mechanism-operator.

One approach toward realizing this objective is illustrated in U.S. Patent 3,065,317-Streater, assigned to the assignee of the present invention. In the circuit breaker of the Streater patent magnetic means is provided for developing a closing, or hold-closed, force on the movable contact that varies directly with current and is present whenever current is flowing through the contacts. While this particular magnetic means does permit a substantial reduction in the closing force requirement for the closing mechanism and operator, it is subject to the disadvantage that a relatively large opening force is needed to overcome the high magnetic closing force when it is desired to open the circuit breaker. In addition, the high magnetic closing force tends to detract from the speed of opening.

Accordingly, another object of my invention is to provide magnetic means which can provide a high closing force for assisting in closing the circuit breaker and holding it closed when desired, but yet does not significantly increase the force required for opening the circuit breaker when such opening is desired.

In carrying out the invention in one form, I provide a first contact and a second contact that is movable into and out of engagement with the first contact. A substantially rigid conductor is mechanically and electrically coupled to said second contact for carrying current to and from the second contact. Magnetic means 3,3663% Patented Jan. 30, 1968 comprising substantially rigid movable structure is provided for developing a magnetic closing force on said conductor which varies directly in accordance with the current through said contacts. Releasable holding means holds said rigid movable structure in a predetermined first position when the contacts are engaged. Contactopening means operates when the holding means is released to drive said rigid structure into engagement with said conductor, thereby transmitting contact-opening motion to said conductor. Closing is initiated by driving said rigid movable structure into said predetermined first position. Until the rigid movable structure has been moved into substantially said predetermined first position, the conductor is restrained in a position where the contacts are widely separated. But upon movement of said rigid movable structure into substantially said predetermined first position, the restraint on the con ductor is removed and the conductor is driven by suitable biasing means into a position where the contacts engage. Such closing movement of the conductor is assisted by the magnetic closing force developed by said magnetic means when the contacts engage near the end of such closing movement.

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic view, partly in section, showing a circuit breaker embodying one form of my invention. In FIG. 1 the circuit breaker is shown in an open position.

FIG. 2 is a schematic view of the circuit breaker of FIG. 1, but with the parts thereof shown in closed position.

FIG. 3 is a sectional view taken along the line 3--3 of FIG. 2.

FIG. 4 illustrates a modified embodiment of the invention.

FIG. 5 illustrates another modified embodiment of the invention.

Referring now to FIG. 1, there is shown an electric circuit breaker that comprises a pair of separable contacts 11 and 12. The contact 11 is a stationary contact and the contact 12 is a movable contact that is vertically movable into and out of engagement with the stationary contact. In FIG. 1, the contact 12 is shown in its fullyopen position where it is widely spaced from the contact 11. Closing of the circuit breaker is effected by driving contact 12 upward into its position of FIG. 2, where it engages contact 11.

Although this invention, in its broader aspects, is applicable to many different types of circuit breakers, I have shown it embodied in a circuit breaker of the vacuum type. Accordingly, the contacts 11, 12 are shown located inside a highly evacuated envelope 13 comprising a cylindrical insulating casing 14 and upper and lower end caps 8 and 15, respectively, joined thereto by vacuumtight seals 16. The stationary contact 11 is mounted on a stationary conductive rod 9 that is integrally joined to the upper end cap 8. The movable contact 12 is mounted on a conductive operating rod 17 that projects freely through the lower end cap 15. A flexible metal bellows 18 between the lower end cap 15 and the operating rod 17 permits vertical movement of the rod 17 without impairing the vacuum inside the envelope 13.

For carrying current to and from the movable contact 12, a rigid conductive cross-bar 20 is rigidly attached to the conductive operating rod 17 at its lower end. This conductive cross-bar 20 is pivotally mounted at one end on a stationary pivot 21 carried by the lower end cap 15. A conductor 23 is suitably joined to the cross-bar 20 at its opposite end for carrying current to and from the crossbar.

Part of the force for driving the contact 12 upwardly through its closing stroke is derived from a tension spring 24. This tension spring 24-, which is connected between the conductive cross-bar and a fixed point 26, urges the cross-bar 20 in a counterclockwise closing direction. When the interrupter is in its open position of FIG. 1, the cross-bar 20 is restrained in its illustrated position by means of a releasable latch 28 which acts on a latch roller 30 carried by the cross-bar 20. The latch 28 is biased into its illustrated positioned by a torsion spring 31 tending to pivot the latch counterclockwise about its stationary pivot 32. When latch 28 is pivoted in a clockwise direction about pivot 32 by means soon to be described, latch roller 30 is released and spring 24 is free to drive crossbar 20 together with contact 12 through an upward closing stroke.

Near the end of the upward closing stroke of movable contact 12, current will begin flowing through contacts 11, 12 via a path that extends through parts 9, 11, 12, 17, 20 and 23. As pointed out hereinabove, this current produces a magnetic force opposing closing that varies directly in accordance with the square of the current. If only a low current flows, then spring 24 acting alone can provide suflicient force to complete the closing operation against this minor opposition and to maintain the contacts 12 and 11 in engagement. But if the current is a high current, then much higher closing forces are needed to complete the closing operation and to maintain the contacts engaged. For providing this supplemental closing force, I rely, in one form of my invention, upon U-shaped structure 40 of low retentivity magnetizable material, e.g., soft iron. As best shown in FIG. 3, this U-shaped structure 40' or yoke comprises a pair of spaced-apart legs 42 and a bight portion 43 joining the legs. Between the legs 42 is an open-sided recess 44 into which the crossbar 20 moves during a closing operation.

This magnetizable structure 40 acts in the general manner described in the aforesaid Streater patent to provide an upward closing force on the cross-bar 20 that varies in accordance with the square of the current through the cross-bar 20. Briefly summarizing, current flowing through the crossbar 20 creates magnetic flux around the bar which is depicted by the lines of force 41 in FIG. 3. These lines of force follow a magnetic circuit extending through the U-shaped magnetic structure 40 and then across the air gap extending between the legs 42 of the magnetizable structure. In this magnetic curcuit, the air gap is in series with the magnetizable structure 40. The cross-bar 20 is positioned in this air gap when the contact 12 is in its fully-closed position of FIGS. 2 and 3. A conductor located in such an air gap will tend to move into a position wherein the reluctance of the surrounding magnetic circuit is a minimum, and thus there is a tendency for conductor 20 to move upwardly toward the bight 43 of the U-shaped structure 40.

The force tending to move conductor 20 toward the bight 43 varies in magnitude as a direct function of the square of the current through conductor 20. Thus, as the current increases, increased magnetic forces are developed at magnetic structure 40 for driving the contacts fully closed and for holding them closed.

The direction of this magnetic force is independent of the polarity of the current flowing through conductor 20 since, irrespective of the direction of the lines of force traversing the air gap, the position of conductor 20 where the reluctance of the magnetic circuit will be a minimum is still toward the bight 43 of the U-shaped structure 40. The magnitude of this magnetic force depends primarily upon the flux density of the magnetic field in the gap, and this flux density is substantially independent of the polarity of the current. In this latter regard, the low retentivity of the magnetizable material assures that the flux density will be substantially the same for a given value of current, whether such value is negative or positive.

The magnitude of the force urging the cross bar toward bight 43 of U-shaped structure 40 is dependent upon the width of the structure 40 (depicted at W in FIG. 2) and varies as a direct function of this width W. In a preferred form of my invention, this width W is made sufliciently large that the closing force developed at magnetic structure 40 for any given current is greater than the electromagnetic loop forces tending to force the contacts open. Thus, for any given current, a net force is present tending to hold the contacts closed or to drive them closed if not already fully closed. This net force increases as current flowing through the contacts increases. This net closing force will prevent the contacts from being blown open by the magnetic loop forces without requiring any assistance from the closing spring 24. This net force simply urges contact 12 more firmly against stationary contact 11 as the current increases. It the contacts 12 and 11 are not fully closed when current is flowing through the crossbar 20, this net force will move contact 12 into full engagement with contact 11 and hold it there.

For reasons which will soon be explained, the magnetizable structure 40 is a movable member that is movable into its position of FIG. 2 and held in such position prior to movement of the crossbar 20 into its contact-engaged position of FIG. 2. FIG. 1 shows the magnetizable structure 40 in a lowered position that it occupies when the circuit breaker is open. A circuit breaker-closing operation is initiated by driving magnetizable structure 40 upwardly from its open position of FIG. 1 into its closed position of FIG. 2. This upward movement causes magnetizable structure 40 to engage and trip latch 28, thereby allowing tension spring 24 to drive cross-bar 20 and movable contact 12 into their contact-engaged position of FIG. 2, as explained hereinabove.

For transmitting the above-described upward force to magnetizable structure 40, I provide an insulating operating rod 45. This operating rod 45 is rigidly connected to magnetizable structure 49 by means of a U-shaped insulating yoke 46, best shown in FIG. 3. The U-shaped insulating yoke 46 contains a recess 47 that aligns with the recess 44 in the magnetizable member 40. Suitable connecting means (not shown) are provided for rigidly coupling parts 40 and 46 together. An opening spring 48 acts on the operating rod 45 and biases it downwardly toward its position of FIG. 1.

For driving the operating rod 45 and the magnetizable structure 40 into their elevated position of FIG. 2 and for holding them in such position, I provide a mechanically trip-free closing mechanism 50 coupled to the lower end of the insulating operating rod 45. Closing mechanism 50 comprises a pair of toggle links 52 and 54 pivotally joined together at a knee 55. One of the toggle links 52 is pivotally connected at its opposite end to the lower end of the operating rod 45 by means of a pivot pin 56. The other toggle link 54 is pivotally connected by pivot pin 58 to the upper end of a guide link 59. This guide link 59 is pivotally supported at its lower end on a fixed fulcrum 60 and is biased toward its position of FIG. 1 by a suitable reset spring 60a. The pivot pin 58 carries a latch roller 61 which cooperates with a suitable trip latch 62. Trip latch 62 is arranged to be operated in response to predetermined circuit conditions by means of a suitable conventional tripping solenoid 64. Typically, the tripping solenoid 64 is suitably connected to be operated in response to an overcurrent through the power circuit through the breaker.

So long as trip latch 62 remains set, i.e., in its latching position of FIG. 1, toggle 52, 54 is capable of transmitting thrust to movable operating rod 45. Thus, when knee 55 is driven to the right from its position shown in FIG. 1, the toggle 52, .54 is extended and drives operating rod 45 upwardly against the bias of opening spring 48. FIG. 2 illustrates the position of the parts after knee 55 has been moved to the right to effect circuit breaker-closing. This closing motion of knee 55 from it position of FIG. 1 to its position of FIG. 2 is produced by the action of a rotatable cam 70 cooperating with the usual roller 72 which is mounted at the knee 55. When cam 70 is rotated counterclockwise from its position of FIG. 1 to its position of FIG. 2 by a suitable operator (not shown), it drives knee 55 to the right, thereby extending toggle 52, 54 and driving operating rod 45 and magnetizable structure 40 through their upward closing stroke. Cam 70 has a constant radius portion 73 that holds the magnetizable structure in its extreme upward position during the final rotation of cam 70 preceding its entry into the position of FIG. 2.

As previously pointed out, when magnetizable structure 40 nears the end of its upward closing stroke, it trips latch 28, thus allowing tension spring 24 to drive crossbar 20 and movable contact 17 upwardly into their contact-engaged position of FIG. 2. Well ahead of the point at which movable contact 12 engages contact 11, the magnetizable structure 4-0 has been moved through the final portion of its closing stroke and into its uppermost position of FIG. 2, where it is held by knee roller '72 resting on the constant-radius portion 73 of cam '70.

When movable contact 12 touches stationary contact 11 at the end of its closing stroke, the current that flows through cross-bar 20 causes magnetiza-ble structure 40 to develop the above-described closing force on cross-bar 20. As was previously pointed out, this magnetic closing force varies directly in accordance with the square of the current and is made high enough to drive the contact 12 into its final position against any short circuit currents that the circuit breaker will encounter.

The magnetizable member 40 and the insulating yoke 46 that is rigidly coupled thereto may be thought of as constituting substantially rigid movable structure that is releasably held in its position of FIG. 2 by the trip latch 62 and closing cam 70 acting through linkage 50, 4.5.

Tripping open of the circuit breaker is effected by energizing solenoid 64 sufficiently to drive trip latch 62 clockwise about its stationary pivot 65 against the bias of a suitable reset spring 66. Should latch 62 be tripped when the circuit breaker is closed, or even during a closing stroke, the pivot 58 will be freed by such tripping action, thus no longer serving as a stationary reaction point for toggle 52, 54. This will render toggle 52, 54 inoperable to transmit thrust to movable operating rod 45, and as a result, opening spring 48 will be free to drive operating rod 51 downwardly into its open position.

Because the mechanism 50 is of the mechanically tripfree type, it will be apparent that opening can be initiated without moving the cam 70 out of its position of FIG. 2. This is highly desirable because a relatively long time would be required to sufficiently move the cam 76, and this would undesirably delay opening. Relying instead upon the trip latch 62 for collapsing the mechanism 50 to initiate opening enables opening to be initiated much more quickly.

During the tripping-open operation, the rigid movable structure 40, 46 moves downwardly with the operating rod 45, and after a predetermined amount of downward motion, magnetizable member 40 strikes the cross-bar 20. This drives cross-bar 20 in a clockwise opening direction against closing spring 24, thus rapidly disengaging contacts 12 and 11 to open the breaker.

Although magnetizable means 40 tends to hold the contacts in engagement under normal closed-circuit conditions, it does not interfere with the above-described opening and, as a matter of fact, actually aids it. In this regard,

note that when the parts are in their closed position of FIGS. 2 and 3, the magnetic force developed at magnetizable structure 40 acts on the magnetizable yoke 40 in a downward direction. But during this period the magnetizable yoke 40 is prevented from moving downwardly by the closing cam 70 acting on roller 72. However, when trip latch 62 is tripped, this downward force on magnetizable structure 40 is free to accelerate downward motion of magnetizable structure 40 until it impacts against crossbar 20. When magnetizable yoke 40 touches cross-bar 20, the electromagnetic force disappears insofar as the moving system is concerned. Thereafter the opening spring 48 drives cross-bar 20 and contact 12 into their fully open position against the relatively light closing spring 24;. When cross-bar 20 reaches its fully-open positon, hold-open latch 28 falls into place behind roller 30, thus holding the crossbar 20 and movable contact 12 fully open.

It will be apparent from the immediately-preceding paragraph that the opening spring 48 is not required to overcome the magnetic force that holds the contacts closed. As a matter of fact, it is assisted by this force during a tripping operation. It will therefore be apparent that the opening spring 48 can be a relatively light spring. Although the opening Spring must operate against closing spring 24, this does not impose much of a burden on it since the closing spring 24 is also relatively light. In this regard, recall that the closing Spring 24, in producing closing, is not required to overcome any magnetic loop force opposing closing since the force for this latter purpose is derived from magnetizable structure 40.

It should be apparent from the above description that operating mechanism 50 may also be relatively small and weak. All that is required of this mechanism 50 and its operator in terms of closing force is the ability to drive the magnetizable structure 40 from its position of FIG. 1 to its position of FIG. 2 against the opening spring 48. Since, as explained above, the opening spring can be relatively light, the mechanism 50' and its operator are called upon to overcome only a small opposing force. The mechanism 50 and its operator therefore can be small and relatively weak and inexpensive. It is to be understood, however, that mechanism 50 and operating rod 45 must have sufiicient rigidity to be able to hold the magnetizable structure 40 in its position of FIG. 2 against the magnetic closing force developed at 40 tending to move magnetizable structure 40 downward.

The operator (not shown) for mechanism 50 is not required to supply closing force for overcoming the usual magnetic loop force opposing closing since, as explained above, such closing force is supplied entirely by the action of magnetizable structure 40. Since the operator for mechanism 50 is relieved of overcoming these magnetic loop forces, it will be apparent that no more force is required of the mechanism operator when closing under short circuit conditions than when closing under no-load conditions. In either case, all that is required of the operator for mechanism 50 is to drive the magnetizable yoke 40 upwardly from its positon of FIG. 1 to its position of FIG. 2, and this is done before any current flows through the circuit breaker and thus without regard to any magnetic loop forces opposing closing.

A related advantage is that I am not required to dissipate the large excess of energy that is present in most circuit breakers when closing on light currents. In this regard, most circuit breakers have a powerful closing means capable of supplying all the energy needed to close against short circuit currents. When closing against low currents, there is a large amount of excess energy, unused for closing, which must be effectively dissipated to prevent damage to the circuit breaker or other harmful effects. My closing means develops closing energy in direct proportion to the current, and thus there is no large amount of excess energy to dissipate when closing on light currents.

FIG. 4 shows a modified form of the invention, where an overcenter spring is employed instead of latch 28 of FIG. 1 in order to hold the contacts open until the magnetizable structure 40 is driven upwardly into substantially its fully-closed position. This over-center spring has one end connected to the cross-bar 2t) and its other end connected to a carrier link 82 that is pivotally supported on a stationary pivot 84. The connection of spring 80 to cross-bar 20 is through a pin 81, and the connection to carrier link 82 is through a pin 83. The carrier link 82 is coupled to the insulating yoke 46 by means of a pin and slot connection 86, 88. Pin 88 is a transverse pin fixed to the yoke 46 and received in a slot 86 in the carrier link 82.

FIG. 4 illustrates the parts in the fully-open position. When operating rod 45 is driven upwardly (in the same manner as explained relative to FIGS. 1-3) the insulating yoke 46, acting through pin and slot connection 86, 88, drives carrier link 82 in a closing direction about its stationary pivot 84. After a predetermined amount of such closing motion by carrier link 82, spring 80 passes across a line connecting pins 21 and 81. Prior to this instant, the over-center spring was urging the cross-bar 20 in a counterclockwise opening direction about pivot 21. But when the spring 80 passes over-center, the spring acts to drive cross-bar 20 in a counter-clockwise closing direction. This drives movable contact 12 toward engagement with stationary contact 11. Magnetizable structure 40 acts in the same manner as previously explained to supply the closing force to overcome any opposing magnetic loop forces that might be established when the contacts 12, 11 touch at the end of the closing operation.

An opening operation of the interrupter of FIG. 4 is effected in the same manner as described with respect to FIGS. 1-3. More specificially, magnetizable structure 40 is driven downwardly by an opening spring (48 of FIG. 2) to impact against cross-bar 2t) and drive the contacts apart.

The carrier link 82 is reset during such an opening operation by means of the pin and slot connection 86, 88. More specifically, downward motion of insulating yoke 46 is imparted through the pin 88 to carrier link 82 to drive carrier link 82 counterclockwise into its open position of FIG. 4.

It will be apparent that with either of these embodiments, I am able to close the circuit breaker against maximum short circuit currents without requiring any substantial additional energy from the operator for mechanism 50 beyond that required at no-load. With either embodiment, I am able to hold the contacts closed regardless of current magnitude so long as the trip latch 62 remains latched. Nevertheless, I can open the contacts freely regardless of current magnitude once the latch 62 is tripped.

FIG. 5 shows another embodiment of my invention. In the embodiment of FIG. 5, the rigid conductor 20 and the hold-open latch 28 are of substantially the same construction as correspondingly-designated parts in FIGS. 1 and 2, but the magnetic closing-force-producing means is somewhat different. In FIG. 5, this magnetic closingforce-producing means comprises a second rigid conductor 100 that is pivotally mounted on a stationary pivot 102. This second conductor 100 is electrically connected to the first conductor 20 through flexible braid 104 connected between the free ends of rigid conductors 26 and 100. A terminal conductor 23 is provided at the opposite end of conductor 1%. When the interrupter is closed, current can flow between this terminal conductor 23 and the movable contact rod 17 through a U-shaped conductive path that is constituted by the series combination of parts 100, 104, and 20. When the interrupter is open, as shown in FIG. 5, no current flows through this U- shaped path.

A. closing operation is initiated by driving lower conductor 100 upwardly into a predetermined first position where it is rigidly held by closing cam 70, corresponding to cam 70 of FIGS. 1 and 2. In the illustrated form of the invention, this operation is effected by force transmitted through trip-free closing mechanism 59 and an operating rod 45 suitably interconnecting mechanism 50 and conductor 1%. Components 45 and 5t; correspond to identically-designated components in FIGS. 1 and 2. Near the end of its closing stroke, the rigid conductor 1% acts through a yoke'106 to trip the hold-open latch 28. This enables closing spring 24 to drive conductor 20 and movable contact 12 upwardly into their respective contactengaged positions.

In the embodiment of FIG. 5, the magnetic closing force for closing against high currents is derived from the interaction of the magnetic fields about conductors and 20. In this respect, when the contacts touch near the end of a closing stroke; current, in traversing the U- shaped conductive path 100, 104, 28, flows through the adjacent rigid conductors 100 and 20 in opposite directions, as indicated by dotted-line arrows 107. The interaction of the magnetic fields about the oppositely conducting adjacent conductors 108 and 28 produces a magnetic repulsion force that tends to separate the conductors 100 and 20. Since the lower conductor 100 is then latched in its uppermost position by the closing cam 70, this repulsion force acts on the movable conductor 20 to complete its upward closing motion and to maintain the contacts engaged.

The magnitude of this closing force is dependent upon the length of the conductors 2t) and 100 disposed to the right of contact rod 17 and varies as a direct function of this length as well as of the current then flowing through the conductors 20 and 100. In a preferred form of the invention, these conductors 20 and 100 are made sufiiciently long that the closing force developed between conductors 20 and 100 for any given current is greater than the electromagnetic loop forces tending to force the contacts open. As in the embodiments of FIGS. 1-4, a net force is present for any given current tending to hold the contacts closed or to drive them closed if not already closed.

An opening operation is initiated in the embodiment of FIG. 5 by tripping the latch 62. This frees the lower conductor 100 for downward movement. The conductor 100 moves rapidly downward under the bias of opening spring 48 and the additional bias of the magnetic repulsion force between conductors 20 and 100. After a predetermined amount of such downward motion, the yoke 106 strikes the upper conductor 20 to drive it downward through its contact-opening stroke.

Until the yoke 106 engages the conductor 20, the magnetic repulsive force between conductors 26 and 100 acts in a closing direction on the conductor 20 and contact 12; but when the yoke 106 engages conductor 20, the magnetic force disappears insofar as the moving system is concerned. Thereafter, opening spring 48 drives conductor 2i) and contact 12 into their fully-open positions against relatively light closing spring 24. When conductor 28 reaches its fully-open position, latch 28 falls into place behind roller 30, thus holding conductor 20 and movable contact 12 fully open.

In each of the illustrated embodiments, the magnetic force which tended to hold the contacts engaged under normal-closed contact conditions is utilized to assist the opening operation when trip latch 62 is tripped. For example, in FIGS. 14, when latch 62 is tripped, this magnetic force drives the yoke 40 downwardly against conductor 2t), and in FIG. 5 this magnetic force drives the yoke 1% downwardly against conductor 20. Since this magnetic force varies as a direct function of the current then flowing, it will be apparent that an opening force varying directly with current is provided. Providing an opening force that varies directly with current is desirable because the speed of contact-separation normally varies directly with the magnitude of this force. Thus, contactseparation is made to take place at higher speeds for higher currents. This relationship appears to contribute to improved interrupting performance by the interrupter.

This invention has particular applicability to a vacuumtype circuit breaker because under certain conditions the interrupting performance of such circuit breakers appears to be sensitive to the amount of contact pressure that is present immediately before opening. More specifically, it appears that the ability of a vacuum circuit breaker to switch predominantly-capacitive circuits is improved when the contact pressure during this interval is low. Since capacitive circuits typically involve low currents, my circuit breaker normally applies only low pressures during the interval preceding opening and thus will exhibit improved capacitance-switching ability, Despite this improved capacitance-switching ability, there is no impairment of the breakers ability to close and remain closed under high current conditions since closing force varying directly with current is developed, as was pointed out hereinabove. In the usual circuit breaker, the high force required for high currents is also present during low currents. This latter relationship, if present in a vacuum circuit breaker, appears to detract from the breakers capacitance-switching ability.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit breaker comprising:

(a) a first contact and a second contact movable into and out of engagement with said first contact,

(b) a substantially rigid conductor mechanically and electrically coupled to said second contact for carrying current to and from said second contact and having a closed-circuit position where said contacts are engaged,

(c) magnetic means comprising substantially rigid movable structure for developing a magnetic closing force on said conductor which varies directly in accordance with the current through said contacts,

((1) means including releasable holding means for holding said rigid movable structure in a predetermined first position when said contacts are engaged,

(e) contact-opening means operable when said holding means is released for driving said rigid structure into engagement with said rigid conductor thereby transmitting contact-opening motion to said conductor,

(f) closing means for returning said rigid movable structure to said predetermined first position to initiate a closing operation of said circuit breaker,

(g) restraining means efiective while said rigid mova ble structure is moving through said return travel for holding said conductor in a position where said contacts are Widely separated,

(h) and closure-assisting means for rendering said restraining means inetfective following movement of said rigid movable structure substantially into said predetermined first position and for thereafter driving said rigid conductor into said closed-circuit position where said contacts are engaged.

2. The circuit breaker of claim 1 in which said rigid conductor constitutes a first substantially rigid conductor and said rigid movable structure comprises a second substantially rigid conductor located adjacent said first conductor, means for connecting said first and second rigid conductors in series and for causing current to flow through said adjacent conductors in opposite directions to produce a repulsive magnetic force therebetween which constitutes at least a portion of said magnetic closing force.

3. The circuit breaker of claim 1 in which said substantially rigid movable structure comprises a member of low retentivity magnetizable material forming a portion of the magnetic circuit for flux generated by current flowing through said conductor, said magnetizable member having a recess into which said conductor is movable to decrease the reluctance of said magnetic circuit, said conductor being positioned in said recess when said contacts are engaged, said magnetic circuit containing in series with said magnetizable member a gap in which said conductor is located when positioned in said contact-engaged position within said recess, whereby a magnetic force is then exerted on said conductor tending to hold said contacts engaged.

4. The circuit breaker of claim 1 in which said rigid movable structure comprises a member of low retentivity magnetic material toward which said conductor is magnetically biased when located adjacent said magnetizable member and carrying current.

5. The circuit breaker of claim 1 in which said closureassisting means comprises means responsive to movement of said rigid movable structure substantially into said predetermined first position.

6. The circuit breaker of claim 1 in which:

(a) said restraining means comprises a hold-open latch for holding said conductor in said contact-separated position, and

(b) said closure-assisting means comprises means for releasing said hold-open latch in response to movement of said rigid movable structure substantially into said predetermined first position.

7. The circuit breaker of claim 1 in which said restraining means and said closure-assisting means comprise an overcenter spring that biases said conductor toward said contact-separated position during initial closing movement of said rigid movable structure toward said predetermined first position but biases said conductor toward said contact-engaged position when said rigid movable structure has moved substantially into said predetermined first position.

8. The circuit breaker of claim 1 in which said closing means comprises a mechanically trip-free linkage coupled to said rigid movable structure; said linkage comprising a releasable latch which, when set, maintains said linkage in a condition to transmit holding force to said rigid movable structure for holding said rigid movable structure in said predetermined first position; said latch, when released, rendering said linkage inefiective to transmit said holding force to said rigid movable structure.

9. The circuit breaker of claim 1 in which said circuit breaker is a vacuum-type circuit breaker comprising a highly-evacuated envelope in which said contacts are located.

10. The circuit breaker of claim 1 in which, upon release of said holding means, said rigid movable structure is driven into engagement with said conductor with a contact-opening force that varies directly in accordance with current then flowing through said contacts.

11. An electric circuit breaker comprising:

(a) a first contact and a second contact movable into and out of engagement with said first contact,

(b) a substantially rigid conductor mechanically and electrically coupled to said second contact for carrying current to and from said second contact,

(c) substantially rigid movable structure including a member of low retentivity magnetizable material forming a portion of the magnetic circuit for flux generated by current flowing through said conductor, said magnetizable member having a recess into which said conductor is movable to decrease the reluctance of said magnetic circuit,

(d) means including releasable holding means for holding said magnetizable member in a predetermined first position wherein said conductor is positioned in said recess when said contacts are engaged,

(c) said magnetic circuit containing in series with said magnetizable member a gap in which said conductor is located when positioned in said contact-engaged position within said recess, whereby a magnetic force is then exerted on said conductor tending to hold said contacts engaged,

(f) contact-opening means operable when said holding means is released for driving said rigid movable structure into engagement with said conductor, thereby transmitting contact-opening motion to said conductor through said rigid movable structure,

(g) closing means for returning said magnetizable member to said predetermined first position to initiate a closing operation of said circuit breaker,

(h) restraining means effective while said magnetizable member is moving through said return travel for holding said conductor in a position where the contacts are widely separated,

(i) and closure-assisting means for rendering said restraining means ineffective following movement of said magnetizable member substantially into said predetermined first position and for thereafter driving said rigid conductor into said contact-engaged position within said recess.

12. An electric circuit breaker of the vacuum-type comprising:

(a) .a first contact and a second contact movable into and out of engagement with said first contact,

(b) a highly evacuated envelope enclosing said contacts,

(c) a rigid conductor outside said envelope mechanically and electrically coupled to said second contact for carrying current to and from said second contact,

(d) magnetic means for developing a magnetic closing force on said conductor which varies directly in accordance with the current through said contacts,

(e) opening means for substantially eliminating said magnetic closing force while current is still flowing through said contacts, thereby reducing the force required for separating said contacts, and

(f) means for rendering said magnetic means effective during a circuit breaker-closing operation to develop said magnetic closing force when a current path is first established through said contacts during closing.

References Cited UNITED STATES PATENTS 2,090,519 8/1937 Rankin 33516 2,601,484 6/1952 Wood 335-16 3,215,797 12/1965 Kesselring et a1 335-192 3,253,098 5/1966 Perry 335-192 BERNARD A GILHEANY, Primary Examiner.

H. BROOME, Assistant Examiner. 

12. AN ELECTRIC CIRCUIT BREAKER OF THE VACUUM-TYPE COMPRISING: (A) A FIRST CONTACT AND A SECOND CONTACT MOVABLE INTO AND OUT OF ENGAGEMENT WITH SAID FIRST CONTACT, (B) A HIGHLY EVACUATED ENVELOPE ENCLOSING SAID CONTACTS, (C) A RIGID CONDUCTOR OUTSIDE SAID ENVELOPE MECHANICALLY AND ELECTRICALLY COUPLED TO SAID SECOND CONTACT FOR CARRYING CURRENT TO AND FROM SAID SECOND CONTACT, (D) MAGNETIC MEANS FOR DEVELOPING A MAGNETIC CLOSING FORCE ON SAID CONDUCTOR WHICH VARIES DIRECTLY IN ACCORDANCE WITH THE CURRENT THROUGH SAID CONTACTS, (E) OPENING MEANS FOR SUBSTANTIALLY ELIMINATING SAID MAGNETIC CLOSING FORCE WHILE CURRENT IS STILL FLOWING THROUGH SAID CONTACTS, THEREBY REDUCING THE FORCE REQUIRED FOR SEPARATING SAID CONTACTS, AND (F) MEANS FOR RENDERING SAID MAGNETIC MEANS EFFECTIVE DURING A CIRCUIT BREAKER-CLOSING OPERATION TO DEVELOP SAID MAGNETIC CLOSING FORCE WHEN A CURRENT PATH IS FIRST ESTABLISHED THROUGH SAID CONTACTS DURING CLOSING. 